March 28, 2008

Aurora Audibility

Stupid Question ™
Nov. 28, 2002
By John Ruch
© 2002

Q: Is it true you can hear the aurora?

A: There are hundreds of reports going back to Roman times of the aurora borealis (or Northern Lights) producing sounds. (I could find no reports for the less-seen Southern Lights.) The idea is also part of Inuit (Eskimo) folklore.

The problem: aurorae occur at 35 to 600 miles up, so far away and in such thin air that they would transmit no audible sounds to the ground if they made any, which they don’t.

Also, while a few supposed recordings have been made, none has been definitively shown to be anything except background noise.

So either people are mistaken or nature has something new to teach us. (And not just about aurorae—similar sounds have been reported with brightly glowing meteors.)

Aurorae are writhing, pulsing areas of light in the sky centered on the magnetic poles. They are produced when charged particles blown off the Sun are trapped in the Earth’s magnetic field and ionize air molecules, causing them to glow.

Ionization is basically an electrical phenomenon, so it’s interesting that reported auroral sounds resemble electronic static: hissing, crackling, ringing, swishing, whistling, rustling like tissue paper or cellophane.

Reports of sound are rare, even among people who have seen aurorae multiple times. Typically, the sound is said to rise and fall in unison with changes in the aurora’s intensity, and to occur simultaneously with it.
Also common is for only one person in a group to hear any sound. The Royal Astronomical Society of Canada in 1928 reported an unscientific test in which members of a government survey team blindfolded one of their fellows who said he could hear an aurora; he reportedly accurately identified changes in its brightness by ear.

Some claims strain credibility. One advanced by the great scientist Antoine Henri Becquerel claimed the sound came with a sulfurous smell.

The sound could be an illusion or wishful thinking. It could be tinnitus only noticed while quietly watching the aurora, or it could be sound of freezing breath moisture, cracking ice or crunching snow.

Aurorae do produce very low frequency radio waves that, if run through a radio amplifier, make whistles and crackles similar to some of the sound reports. (I have heard recordings of this radio noise and it is eerie.) One theory is that something in nature, even in the human body, picks up these waves and turns them into sound. What and how are unknown.

Aurorae also increase the general electric charge of the air at ground level, though minutely. Some speculate that this causes miniature sparks that create the sound. But surely some of these sparks would be visible, and they have never been reported.

According to extremely rare reports that are anomalies within an anomaly (and pure scientific heresy), the distance of the aurorae isn’t always a problem. They claim seeing aurorae dipping to just a few thousand feet, or even ground level, with the observer walking through a glowing white fog filled with flashing colors, while the auroral sound crackles all around.

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